1. Field of the Invention
The present invention relates to a spring which is highly strong so that it is capable of enduring a severe fatigue loading and more specifically to a high strength spring suited for use as a valve spring for an internal combustion engine.
2. Description of the Prior Art
Of the prior art high strength springs, a valve spring for an internal combustion engine has heretofore been made of a material as, for example, SWO-V (spring steel wire according to JIS G3561, i.e., Japanese Industrial Standard G3561), SWOCV-V (spring steel wire according JIS G3565 and SWOSC-V (spring steel wire according to JIS G3566).
To this end, it has recently begun to use o super SWOSC-V (hereinafter referred to as SWOSC-V*) which is improved in strength and attained by further reducing the content of the inclusions in the above described SWOSC-V.
While SWOSC-V* is considerably improved in strength as compared with SWOSC-V, it is still insufficient in strength in order to satisfactorily improve a valve drive train in maximum operation speed and friction for thereby attaining a desired high efficiency and low fuel comsumption of an associated engine. It is therefore eagerly desired to develop a new valve spring which is compact in size, light in weight and of a high strength as well as being stable in quality and highly reliable in operation.